Seven bridges spanned the River Pregel,
Many more than might have been expected;
Königsberg’s wise leaders were delighted
To have built such very splendid structures.
Crowds each ev’ning surged towards the river,
People walked bemused across the bridges,
Pondering a simple-sounding challenge
Which defeated them and left them puzzled.
Here’s the problem; see if you can solve it!
Try it out at home an scraps of paper!
STARTING OUT AND ENDING AT THE SAME SPOT,
YOU MUST CROSS EACH BRIDGE JUST ONCE EACH EV’NING.
Eulerian graphs all have this restriction:
THE DEGREE OF ANY POINT IS EVEN.
That’s the oldest graph result
That mankind has ever known.
All the folk in Königsberg were frantic!
All their efforts ended up in failure!
Happily, a learn-ed math’matician
Had his house right there within the city.
Euler’s mind was equal to the problem:
“Ah”, he said, “You’re bound to be disheartened.
Crossing each bridge only once per outing
Can’t be done, I truly do assure you.”
Laws of Nature never can be altered,
We can’d change them, even if we wish to.
Nor can flooded rivers or great bridges
Interfere with scientific progress.
War brought strife and ruin to the Pregel;
Bombs destroyed those seven splendid bridges.
Euler’s name and fame will, notwithstanding,
Be recalled with Königsberg’s for ever.
Thanks to Euler, Graph Thry is thriving.
Year by year it flourishes and blossoms,
Fertilising much of mathematics
And so rich in all its applications.
Colleagues, let us fill up all our glasses!
Colleagues, let us raise them now to toast the
Greatness and the everlasting glory
Of our Graph Thry, which we love dearly!